The Trinidad & Tobago striker suffered a nasty elbow injury just 35 minutes into his debut against Plymouth Argyle on Saturday and is facing a spell on the sidelines.
Alan Lee came on for John and grabbed Palace's equaliser in the 1-1 draw to put himself in the frame for a start against Paul Buckle's Gulls at Selhurst Park
Summer signing Darren Ambrose made a 30-minute cameo to prove his fitness after a shoulder injury suffered in pre-season and could be in line for his full debut.
Jose Fonte's thigh injury will be checked over while Palace are still awaiting a work permit for fellow defender Claude Davis.
The match kicks off at 7.30pm.